A mortgage calculator estimates the regular repayment amount on a home loan based on the principal borrowed, the annual interest rate, the loan term and how often you make payments. It uses the standard amortisation formula to show you exactly what each payment covers and how much interest you will pay over the life of the loan.

1. Enter the loan amount (principal).
2. Enter the annual interest rate as a percentage.
3. Enter the loan term in years.
4. Select your payment frequency.
5. Click Calculate.

Loan: $400,000 at 6.5% p.a. over 25 years, paid monthly.
Monthly rate r = 6.5% ÷ 12 = 0.5417%
n = 25 × 12 = 300 payments
Monthly payment ≈ $2,697 | Total interest ≈ $409,100 | Total repayment ≈ $809,100

The result shows your estimated regular payment. Early in the loan most of each payment covers interest; over time more goes toward the principal. Increasing your payment frequency (e.g. fortnightly instead of monthly) can reduce total interest paid because you make the equivalent of one extra monthly payment per year.

• Confusing the nominal rate with the comparison rate — use the rate that applies to your specific loan.
• Forgetting that fees, insurance and offset accounts affect the real cost.
• Using the wrong payment frequency — fortnightly is not simply monthly ÷ 2.

Does this include fees?

No. The calculator uses only the values you enter. Real mortgages may include establishment fees, ongoing fees and lenders mortgage insurance which will increase the total cost.

What is the difference between principal and interest vs interest only?

This calculator uses principal and interest repayments, where each payment reduces the loan balance. Interest-only loans have lower initial payments but the principal does not reduce during the interest-only period.

How does payment frequency affect total interest?

Paying fortnightly (26 payments/year) is equivalent to making 13 monthly payments per year. The extra payment reduces the principal faster, cutting total interest paid.